Inkjet printhead chip with volume-reduction actuation

ABSTRACT

An inkjet printhead chip includes a wafer substrate. A drive circuitry layer is positioned on the wafer substrate. A plurality of nozzle chambers is defined in the wafer substrate. A plurality of ink inlet openings is defined in the wafer substrate, in fluid communication with respective nozzle chambers. A plurality of nozzle chamber walls is opposite respective ink inlet openings and each defines an ink ejection port. A plurality of ink ejection actuators is connected to the drive circuitry layer. At least one actuator is positioned in each wall and is displaceable into the respective nozzle chamber to reduce a volume of the nozzle chamber and thus to eject ink from the nozzle chamber.

This is a Continuation of 09/854,830 filed May 15, 2001 which is aContinuation of U.S. Pat. No. 6,247,790 all of which are hereinincorporated by reference.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are herebyincorporated by cross-reference. For the purposes of location andidentification, US patent applications identified by their US patentapplication serial numbers (USSN) are listed alongside the Australianapplications from which the US patent applications claim the right ofpriority. US PATENT/PATENT CROSS-REFERENCED APPLICATION (CLAIMINGAUSTRALIAN RIGHT OF PRIORITY FROM PROVISIONAL PATENT AUSTRALIANPROVISIONAL DOCKET APPLICATION NO. APPLICATION) NO. PO7991 6,750,901ART01 PO8505 6,476,863 ART02 PO7988 6,788,336 ART03 PO9395 6,322,181ART04 PO8017 6,597,817 ART06 PO8014 6,227,648 ART07 PO8025 6,727,948ART08 PO8032 6,690,419 ART09 PO7999 6,727,951 ART10 PO7998 09/112,742ART11 PO8031 09/112,741 ART12 PO8030 6,196,541 ART13 PO7997 6,195,150ART15 PO7979 6,362,868 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067ART18 PO7982 6,431,669 ART19 PO7989 6,362,869 ART20 PO8019 6,472,052ART21 PO7980 6,356,715 ART22 PO8018 09/112,777 ART24 PO7938 6,636,216ART25 PO8016 6,366,693 ART26 PO8024 6,329,990 ART27 PO7940 09/113,072ART28 PO7939 6,459,495 ART29 PO8501 6,137,500 ART30 PO8500 6,690,416ART31 PO7987 09/113,071 ART32 PO8022 6,398,328 ART33 PO8497 09/113,090ART34 PO8020 6,431,704 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786ART42 PO8000 6,415,054 ART43 PO7977 09/112,782 ART44 PO7934 6,665,454ART45 PO7990 6,542,645 ART46 PO8499 6,486,886 ART47 PO8502 6,381,361ART48 PO7981 6,317,192 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054ART52 PO8026 6,646,757 ART53 PO8027 09/112,759 ART54 PO8028 6,624,848ART56 PO9394 6,357,135 ART57 PO9396 09/113,107 ART58 PO9397 6,271,931ART59 PO9398 6,353,772 ART60 PO9399 6,106,147 ART61 PO9400 6,665,008ART62 PO9401 6,304,291 ART63 PO9402 09/112,788 ART64 PO9403 6,305,770ART65 PO9405 6,289,262 ART66 PP0959 6,315,200 ART68 PP1397 6,217,165ART69 PP2370 6,786,420 DOT01 PP2371 09/113,052 DOT02 PO8003 6,350,023Fluid01 PO8005 6,318849 Fluid02 PO9404 09/113,101 Fluid03 PO80666,227,652 IJ01 PO8072 6,213,588 IJ02 PO8040 6,213,589 IJ03 PO80716,231,163 IJ04 PO8047 6,247,795 IJ05 PO8035 6,394,581 IJ06 PO80446,244,691 IJ07 PO8063 6,257,704 IJ08 PO8057 6,416,168 IJ09 PO80566,220,694 IJ10 PO8069 6,257,705 IJ11 PO8049 6,247,794 IJ12 PO80366,234,610 IJ13 PO8048 6,247,793 IJ14 PO8070 6,264,306 IJ15 PO80676,241,342 IJ16 PO8001 6,247,792 IJ17 PO8038 6,264,307 IJ18 PO80336,254,220 IJ19 PO8002 6,234,611 IJ20 PO8068 6,302,528 IJ21 PO80626,283,582 IJ22 PO8034 6,239,821 IJ23 PO8039 6,338,547 IJ24 PO80416,247,796 IJ25 PO8004 6,557,977 IJ26 PO8037 6,390,603 IJ27 PO80436,362,843 IJ28 PO8042 6,293,653 IJ29 PO8064 6,312,107 IJ30 PO93896,227,653 IJ31 PO9391 6,234,609 IJ32 PP0888 6,238,040 IJ33 PP08916,188,415 IJ34 PP0890 6,227,654 IJ35 PP0873 6,209,989 IJ36 PP09936,247,791 IJ37 PP0890 6,336,710 IJ38 PP1398 6,217,153 IJ39 PP25926,419,167 IJ40 PP2593 6,243,113 IJ41 PP3991 6,283,581 IJ42 PP39876,247,790 IJ43 PP3985 6,260,953 IJ44 PP3983 6,267,469 IJ45 PO79356,224,780 IJM01 PO7936 6,235,212 IJM02 PO7937 6,280,643 IJM03 PO80616,284,147 IJM04 PO8054 6,214,244 IJM05 PO8065 6,071,750 IJM06 PO80556,267,905 IJM07 PO8053 6,251,298 IJM08 PO8078 6,258,285 IJM09 PO79336,225,138 IJM10 PO7950 6,241,904 IJM11 PO7949 6,299,786 IJM12 PO806009/113,124 IJM13 PO8059 6,231,773 IJM14 PO8073 6,190,931 IJM15 PO80766,248,249 IJM16 PO8075 6,290,862 IJM17 PO8079 6,241,906 IJM18 PO80506,565,762 IJM19 PO8052 6,241,905 IJM20 PO7948 6,451,216 IJM21 PO79516,231,772 IJM22 PO8074 6,274,056 IJM23 PO7941 6,290,861 IJM24 PO80776,248,248 IJM25 PO8058 6,306,671 IJM26 PO8051 6,331,258 IJM27 PO80456,111,754 IJM28 PO7952 6,294,101 IJM29 PO8046 6,416,679 IJM30 PO93906,264,849 IJM31 PO9392 6,254,793 IJM32 PP0889 6,235,211 IJM35 PP08876,491,833 IJM36 PP0882 6,264,850 IJM37 PP0874 6,258,284 IJM38 PP13966,312,615 IJM39 PP3989 6,228,668 IJM40 PP2591 6,180,427 IJM41 PP39906,171,875 IJM42 PP3986 6,267,904 IJM43 PP3984 6,245,247 IJM44 PP39826,315,914 IJM45 PP0895 6,231,148 IR01 PP0870 09/113,106 IR02 PP08696,293,658 IR04 PP0887 6,614,560 IR05 PP0885 6,238,033 IR06 PP08846,312,070 IR10 PP0886 6,238,111 IR12 PP0871 09/113,086 IR13 PP087609/113,094 IR14 PP0877 6,378,970 IR16 PP0878 6,196,739 IR17 PP087909/112,774 IR18 PP0883 6,270,182 IR19 PP0880 6,152,619 IR20 PP088109/113,092 IR21 PO8006 6,087,638 MEMS02 PO8007 6,340,222 MEMS03 PO800809/113,062 MEMS04 PO8010 6,041,600 MEMS05 PO8011 6,299,300 MEMS06 PO79476,067,797 MEMS07 PO7944 6,286,935 MEMS09 PO7946 6,044,646 MEMS10 PO939309/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 6,382,769 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the field of inkjet printing and, inparticular, discloses an inverted radial back-curling thermoelastic inkjet printing mechanism.

BACKGROUND OF THE INVENTION

Many different types of printing mechanisms have been invented, a largenumber of which are presently in use. The known forms of printers have avariety of methods for marking the print media with a relevant markingmedia. Commonly used forms of printing include offset printing, laserprinting and copying devices, dot matrix type impact printers, thermalpaper printers, film recorders, thermal wax printers, dye sublimationprinters and ink jet printers both of the drop on demand and continuousflow type. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles, has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques of ink jet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different forms. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including a step wherein the ink jet streamis modulated by a high frequency electro-static field so as to causedrop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al).

Piezoelectric ink jet printers are also one form of commonly utilizedink jet printing device. Piezoelectric systems are disclosed by Kyseret. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragmmode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) whichdiscloses a squeeze mode form of operation of a piezoelectric crystal,Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend mode ofpiezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 whichdiscloses a piezoelectric push mode actuation of the ink jet stream andFischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode typeof piezoelectric transducer element.

Recently, thermal ink jet printing has become an extremely popular formof ink jet printing. The ink jet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclose ink jetprinting techniques which rely on the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Printing devices utilizing the electro-thermal actuator are manufacturedby manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high speed operation, safe and continuous long termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction and operation, durability andconsumables.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there isprovided a nozzle arrangement for an ink jet printhead, the arrangementcomprising: a nozzle chamber defined in a wafer substrate for thestorage of ink to be ejected; an ink ejection port having a rim formedon one wall of the chamber; and a series of actuators attached to thewafer substrate, and forming a portion of the wall of the nozzle chamberadjacent the rim, the actuator paddles further being actuated in unisonso as to eject ink from the nozzle chamber via the ink ejection nozzle.

The actuators can include a surface which bends inwards away from thecentre of the nozzle chamber upon actuation. The actuators arepreferably actuated by means of a thermal actuator device. The thermalactuator device may comprise a conductive resistive heating elementencased within a material having a high coefficient of thermalexpansion. The element can be serpentine to allow for substantiallyunhindered expansion of the material. The actuators are preferablyarranged radially around the nozzle rim.

The actuators can form a membrane between the nozzle chamber and anexternal atmosphere of the arrangement and the actuators bend away fromthe external atmosphere to cause an increase in pressure within thenozzle chamber thereby initiating a consequential ejection of ink fromthe nozzle chamber. The actuators can bend away from a central axis ofthe nozzle chamber.

The nozzle arrangement can be formed on the wafer substrate utilizingmicro-electro mechanical techniques and further can comprise an inksupply channel in communication with the nozzle chamber. The ink supplychannel may be etched through the wafer. The nozzle arrangement mayinclude a series of struts which support the nozzle rim.

The arrangement can be formed adjacent to neighbouring arrangements soas to form a pagewidth printhead.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIGS. 1-3 are schematic sectional views illustrating the operationalprinciples of the preferred embodiment;

FIG. 4(a) and FIG. 4(b) are again schematic sections illustrating theoperational principles of the thermal actuator device;

FIG. 5 is a side perspective view, partly in section, of a single nozzlearrangement constructed in accordance with the preferred embodiments;

FIGS. 6-13 are side perspective views, partly in section, illustratingthe manufacturing steps of the preferred embodiments;

FIG. 14 illustrates an array of ink jet nozzles formed in accordancewith the manufacturing procedures of the preferred embodiment;

FIG. 15 provides a legend of the materials indicated in FIGS. 16 to 23;and

FIG. 16 to FIG. 23 illustrate sectional views of the manufacturing stepsin one form of construction of a nozzle arrangement in accordance withthe invention.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, ink is ejected out of a nozzle chamber viaan ink ejection port using a series of radially positioned thermalactuator devices that are arranged about the ink ejection port and areactivated to pressurize the ink within the nozzle chamber therebycausing the ejection of ink through the ejection port.

Turning now to FIGS. 1, 2 and 3, there is illustrated the basicoperational principles of the preferred embodiment. FIG. 1 illustrates asingle nozzle arrangement 1 in its quiescent state. The arrangement 1includes a nozzle chamber 2 which is normally filled with ink so as toform a meniscus 3 in an ink ejection port 4. The nozzle chamber 2 isformed within a wafer 5. The nozzle chamber 2 is supplied with ink viaan ink supply channel 6 which is etched through the wafer 5 with ahighly isotropic plasma etching system. A suitable etcher can be theAdvance Silicon Etch (ASE) system available from Surface TechnologySystems of the United Kingdom.

A top of the nozzle arrangement 1 includes a series of radiallypositioned actuators 8, 9. These actuators comprise apolytetrafluoroethylene (PTFE) layer and an internal serpentine coppercore 17. Upon heating of the copper core 17, the surrounding PTFEexpands rapidly resulting in a generally downward movement of theactuators 8, 9. Hence, when it is desired to eject ink from the inkejection port 4, a current is passed through the actuators 8, 9 whichresults in them bending generally downwards as illustrated in FIG. 2.The downward bending movement of the actuators 8, 9 results in asubstantial increase in pressure within the nozzle chamber 2. Theincrease in pressure in the nozzle chamber 2 results in an expansion ofthe meniscus 3 as illustrated in FIG. 2.

The actuators 8, 9 are activated only briefly and subsequentlydeactivated. Consequently, the situation is as illustrated in FIG. 3with the actuators 8, 9 returning to their original positions. Thisresults in a general inflow of ink back into the nozzle chamber 2 and anecking and breaking of the meniscus 3 resulting in the ejection of adrop 12. The necking and breaking of the meniscus 3 is a consequence ofthe forward momentum of the ink associated with drop 12 and the backwardpressure experienced as a result of the return of the actuators 8, 9 totheir original positions. The return of the actuators 8,9 also resultsin a general inflow of ink from the channel 6 as a result of surfacetension effects and, eventually, the state returns to the quiescentposition as illustrated in FIG. 1.

FIGS. 4(a) and 4(b) illustrate the principle of operation of the thermalactuator. The thermal actuator is preferably constructed from a material14 having a high coefficient of thermal expansion. Embedded within thematerial 14 are a series of heater elements 15 which can be a series ofconductive elements designed to carry a current. The conductive elements15 are heated by passing a current through the elements 15 with theheating resulting in a general increase in temperature in the areaaround the heating elements 15. The position of the elements 15 is suchthat uneven heating of the material 14 occurs. The uneven increase intemperature causes a corresponding uneven expansion of the material 14.Hence, as illustrated in FIG. 4(b), the PTFE is bent generally in thedirection shown.

In FIG. 5, there is illustrated a side perspective view of oneembodiment of a nozzle arrangement constructed in accordance with theprinciples previously outlined. The nozzle chamber 2 is formed with anisotropic surface etch of the wafer 5. The wafer 5 can include a CMOSlayer including all the required power and drive circuits. Further, theactuators 8, 9 each have a leaf or petal formation which extends towardsa nozzle rim 28 defining the ejection port 4. The normally inner end ofeach leaf or petal formation is displaceable with respect to the nozzlerim 28. Each activator 8, 9 has an internal copper core 17 defining theelement 15. The core 17 winds in a serpentine manner to provide forsubstantially unhindered expansion of the actuators 8, 9. The operationof the actuators 8, 9 is as illustrated in FIG. 4(a) and FIG. 4(b) suchthat, upon activation, the actuators 8 bend as previously describedresulting in a displacement of each petal formation away from the nozzlerim 28 and into the nozzle chamber 2. The ink supply channel 6 can becreated via a deep silicon back edge of the wafer 5 utilizing a plasmaetcher or the like. The copper or aluminium core 17 can provide acomplete circuit. A central arm 18 which can include both metal and PTFEportions provides the main structural support for the actuators 8, 9.

Turning now to FIG. 6 to FIG. 13, one form of manufacture of the nozzlearrangement 1 in accordance with the principles of the preferredembodiment is shown. The nozzle arrangement 1 is preferably manufacturedusing microelectromechanical (MEMS) techniques and can include thefollowing construction techniques:

As shown initially in FIG. 6, the initial processing starting materialis a standard semi-conductor wafer 20 having a complete CMOS level 21 toa first level of metal. The first level of metal includes portions 22which are utilized for providing power to the thermal actuators 8, 9.

The first step, as illustrated in FIG. 7, is to etch a nozzle regiondown to the silicon wafer 20 utilizing an appropriate mask.

Next, as illustrated in FIG. 8, a 2 μm layer of polytetrafluoroethylene(PTFE) is deposited and etched so as to define vias 24 forinterconnecting multiple levels.

Next, as illustrated in FIG. 9, the second level metal layer isdeposited, masked and etched to define a heater structure 25. The heaterstructure 25 includes via 26 interconnected with a lower aluminiumlayer.

Next, as illustrated in FIG. 10, a further 2 μm layer of PTFE isdeposited and etched to the depth of 1 μm utilizing a nozzle rim mask todefine the nozzle rim 28 in addition to ink flow guide rails 29 whichgenerally restrain any wicking along the surface of the PTFE layer. Theguide rails 29 surround small thin slots and, as such, surface tensioneffects are a lot higher around these slots which in turn results inminimal outflow of ink during operation.

Next, as illustrated in FIG. 11, the PTFE is etched utilizing a nozzleand actuator mask to define a port portion 30 and slots 31 and 32.

Next, as illustrated in FIG. 12, the wafer is crystallographicallyetched on a <111> plane utilizing a standard crystallographic etchantsuch as KOH. The etching forms a chamber 33, directly below the portportion 30.

In FIG. 13, the ink supply channel 34 can be etched from the back of thewafer utilizing a highly anisotropic etcher such as the STS etcher fromSilicon Technology Systems of United Kingdom. An array of ink jetnozzles can be formed simultaneously with a portion of an array 36 beingillustrated in FIG. 14. A portion of the printhead is formedsimultaneously and diced by the STS etching process. The array 36 shownprovides for four column printing with each separate column attached toa different colour ink supply channel being supplied from the back ofthe wafer. Bond pads 37 provide for electrical control of the ejectionmechanism.

In this manner, large pagewidth printheads can be fabricated so as toprovide for a drop-on-demand ink ejection mechanism.

One form of detailed manufacturing process which can be used tofabricate monolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed utilizing thefollowing steps:

-   -   1. Using a double-sided polished wafer 60, complete a 0.5        micron, one poly, 2 metal CMOS process 61. This step is shown in        FIG. 16. For clarity, these diagrams may not be to scale, and        may not represent a cross section though any single plane of the        nozzle. FIG. 15 is a key to representations of various materials        in these manufacturing diagrams, and those of other cross        referenced ink jet configurations.    -   2. Etch the CMOS oxide layers down to silicon or second level        metal using Mask 1. This mask defines the nozzle cavity and the        edge of the chips. This step is shown in FIG. 16.    -   3. Deposit a thin layer (not shown) of a hydrophilic polymer,        and treat the surface of this polymer for PTFE adherence.    -   4. Deposit 1.5 microns of polytetrafluoroethylene (PTFE) 62.    -   5. Etch the PTFE and CMOS oxide layers to second level metal        using Mask 2. This mask defines the contact vias for the heater        electrodes. This step is shown in FIG. 17.    -   6. Deposit and pattern 0.5 microns of gold 63 using a lift-off        process using Mask 3. This mask defines the heater pattern. This        step is shown in FIG. 18.    -   7. Deposit 1.5 microns of PTFE 64.    -   8. Etch 1 micron of PTFE using Mask 4. This mask defines the        nozzle rim 65 and the rim at the edge 66 of the nozzle chamber.        This step is shown in FIG. 19.    -   9. Etch both layers of PTFE and the thin hydrophilic layer down        to silicon using Mask 5. This mask defines a gap 67 at inner        edges of the actuators, and the edge of the chips. It also forms        the mask for a subsequent crystallographic etch. This step is        shown in FIG. 20.    -   10. Crystallographically etch the exposed silicon using KOH.        This etch stops on <111> crystallographic planes 68, forming an        inverted square pyramid with sidewall angles of 54.74 degrees.        This step is shown in FIG. 21.    -   11. Back-etch through the silicon wafer (with, for example, an        ASE Advanced Silicon Etcher from Surface Technology Systems)        using Mask 6. This mask defines the ink inlets 69 which are        etched through the wafer. The wafer is also diced by this etch.        This step is shown in FIG. 22.    -   12. Mount the printheads in their packaging, which may be a        molded plastic former incorporating ink channels which supply        the appropriate color ink to the ink inlets 69 at the back of        the wafer.    -   13. Connect the printheads to their interconnect systems. For a        low profile connection with minimum disruption of airflow, TAB        may be used. Wire bonding may also be used if the printer is to        be operated with sufficient clearance to the paper.    -   14. Fill the completed print heads with ink 70 and test them. A        filled nozzle is shown in FIG. 23.

The presently disclosed ink jet printing technology is potentiallysuited to a wide range of printing systems including: color andmonochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable color and monochrome printers, color andmonochrome copiers, color and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic“minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Ofcourse many different devices could be used. However presently popularink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption.This is approximately 100 times that required for high speed, and stemsfrom the energy-inefficient means of drop ejection. This involves therapid boiling of water to produce a vapor bubble which expels the ink.Water has a very high heat capacity, and must be superheated in thermalink jet applications. This leads to an efficiency of around 0.02%, fromelectricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per printhead, but is a majorimpediment to the fabrication of pagewidth printheads with 19,200nozzles.

Ideally, the ink jet technologies used meet the stringent requirementsof in-camera digital color printing and other high quality, high speed,low cost printing applications. To meet the requirements of digitalphotography, new ink jet technologies have been created. The targetfeatures include:

-   -   low power (less than 10 Watts)    -   high resolution capability (1,600 dpi or more)    -   photographic quality output    -   low manufacturing cost    -   small size (pagewidth times minimum cross section)    -   high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systemsdescribed below with differing levels of difficulty. Forty-fivedifferent ink jet technologies have been developed by the Assignee togive a wide range of choices for high volume manufacture. Thesetechnologies form part of separate applications assigned to the presentAssignee as set out in the table below under the heading CrossReferences to Related Applications.

The ink jet designs shown here are suitable for a wide range of digitalprinting systems, from battery powered one-time use digital cameras,through to desktop and network printers, and through to commercialprinting systems.

For ease of manufacture using standard process equipment, the printheadis designed to be a monolithic 0.5 micron CMOS chip with MEMS postprocessing. For color photographic applications, the printhead is 100 mmlong, with a width which depends upon the ink jet type. The smallestprinthead designed is IJ38, which is 0.35 mm wide, giving a chip area of35 square mm. The printheads each contain 19,200 nozzles plus data andcontrol circuitry.

Ink is supplied to the back of the printhead by injection molded plasticink channels. The molding requires 50 micron features, which can becreated using a lithographically micromachined insert in a standardinjection molding tool. Ink flows through holes etched through the waferto the nozzle chambers fabricated on the front surface of the wafer. Theprinthead is connected to the camera circuitry by tape automatedbonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation ofindividual ink jet nozzles have been identified. These characteristicsare largely orthogonal, and so can be elucidated as an elevendimensional matrix. Most of the eleven axes of this matrix includeentries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of inkjet types.

-   -   Actuator mechanism (18 types)    -   Basic operation mode (7 types)    -   Auxiliary mechanism (8 types)    -   Actuator amplification or modification method (17 types)    -   Actuator motion (19 types)    -   Nozzle refill method (4 types)    -   Method of restricting back-flow through inlet (10 types)    -   Nozzle clearing method (9 types)    -   Nozzle plate construction (9 types)    -   Drop ejection direction (5 types)    -   Ink type (7 types).

The complete eleven dimensional table represented by these axes contains36.9 billion possible configurations of ink jet nozzle. While not all ofthe possible combinations result in a viable ink jet technology, manymillion configurations are viable. It is clearly impractical toelucidate all of the possible configurations. Instead, certain ink jettypes have been investigated in detail. These are designated IJ01 toIJ45 above which matches the docket numbers in the table under theheading Cross References to Related Applications.

Other ink jet configurations can readily be derived from theseforty-five examples by substituting alternative configurations along oneor more of the 11 axes. Most of the IJ01 to IJ45 examples can be madeinto ink jet printheads with characteristics superior to any currentlyavailable ink jet technology.

Where there are prior art examples known to the inventor, one or more ofthese examples are listed in the examples column of the tables below.The IJ01 to IJ45 series are also listed in the examples column. In somecases, print technology may be listed more than once in a table, whereit shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Homeprinters, Office network printers, Short run digital printers,Commercial print systems, Fabric printers, Pocket printers, Internet WWWprinters, Video printers, Medical imaging, Wide format printers,Notebook PC printers, Fax machines, Industrial printing systems,Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrixare set out in the following tables. ACTUATOR MECHANISM (APPLIED ONLY TOSELECTED INK DROPS) Description Advantages Disadvantages ExamplesThermal An electrothermal Large force High power Canon Bubblejet bubbleheater heats the ink to generated Ink carrier 1979 Endo et al GB aboveboiling point, Simple limited to water patent 2,007,162 transferringsignificant construction Low efficiency Xerox heater-in- heat to theaqueous No moving parts High pit 1990 Hawkins et ink. A bubble Fastoperation temperatures al U.S. Pat. No. 4,899,181 nucleates and quicklySmall chip area required Hewlett-Packard forms, expelling the requiredfor actuator High mechanical TIJ 1982 Vaught et ink. stress al U.S. Pat.No. 4,490,728 The efficiency of the Unusual process is low, withmaterials required typically less than Large drive 0.05% of theelectrical transistors energy being Cavitation causes transformed intoactuator failure kinetic energy of the Kogation reduces drop. bubbleformation Large print heads are difficult to fabricate Piezoelectric Apiezoelectric crystal Low power Very large area Kyser et al U.S. Pat.No. such as lead consumption required for actuator 3,946,398 lanthanumzirconate Many ink types Difficult to Zoltan U.S. Pat. No. (PZT) iselectrically can be used integrate with 3,683,212 activated, and eitherFast operation electronics 1973 Stemme expands, shears, or Highefficiency High voltage U.S. Pat. No. 3,747,120 bends to apply drivetransistors Epson Stylus pressure to the ink, required Tektronixejecting drops. Full pagewidth IJ04 print heads impractical due toactuator size Requires electrical poling in high field strengths duringmanufacture Electrostrictive An electric field is Low power Low maximumSeiko Epson, used to activate consumption strain (approx. Usui et all JPelectrostriction in Many ink types 0.01%) 253401/96 relaxor materialssuch can be used Large area IJ04 as lead lanthanum Low thermal requiredfor actuator zirconate titanate expansion due to low strain (PLZT) orlead Electric field Response speed magnesium niobate strength requiredis marginal (˜10 μs) (PMN). (approx. 3.5 V/μm) High voltage can begenerated drive transistors without difficulty required Does not requireFull pagewidth electrical poling print heads impractical due to actuatorsize Ferroelectric An electric field is Low power Difficult to IJ04 usedto induce a phase consumption integrate with transition between the Manyink types electronics antiferroelectric (AFE) can be used Unusual andferroelectric (FE) Fast operation materials such as phase. Perovskite(<1 μs) PLZSnT are materials such as tin Relatively high requiredmodified lead longitudinal strain Actuators require lanthanum zirconateHigh efficiency a large area titanate (PLZSnT) Electric field exhibitlarge strains of strength of around 3 V/μm up to 1% associated can bereadily with the AFE to FE provided phase transition. ElectrostaticConductive plates are Low power Difficult to IJ02, IJ04 plates separatedby a consumption operate electrostatic compressible or fluid Many inktypes devices in an dielectric (usually air). can be used aqueous Uponapplication of a Fast operation environment voltage, the plates Theelectrostatic attract each other and actuator will displace ink, causingnormally need to be drop ejection. The separated from the conductiveplates may ink be in a comb or Very large area honeycomb structure,required to achieve or stacked to increase high forces the surface areaand High voltage therefore the force. drive transistors may be requiredFull pagewidth print heads are not competitive due to actuator sizeElectrostatic A strong electric field Low current High voltage 1989Saito et al, pull is applied to the ink, consumption required U.S. Pat.No. 4,799,068 on ink whereupon Low temperature May be damaged 1989 Miuraet al, electrostatic attraction by sparks due to air U.S. Pat. No.4,810,954 accelerates the ink breakdown Tone-jet towards the printRequired field medium. strength increases as the drop size decreasesHigh voltage drive transistors required Electrostatic field attractsdust Permanent An electromagnet Low power Complex IJ07, IJ10 magnetdirectly attracts a consumption fabrication electromagnetic permanentmagnet, Many ink types Permanent displacing ink and can be used magneticmaterial causing drop ejection. Fast operation such as Neodymium Rareearth magnets High efficiency Iron Boron (NdFeB) with a field strengthEasy extension required. around 1 Tesla can be from single nozzles Highlocal used. Examples are: to pagewidth print currents required SamariumCobalt heads Copper (SaCo) and magnetic metalization should materials inthe be used for long neodymium iron boron electromigration family(NdFeB, lifetime and low NdDyFeBNb, resistivity NdDyFeB, etc) Pigmentedinks are usually infeasible Operating temperature limited to the Curietemperature (around 540 K) Soft A solenoid induced a Low power ComplexIJ01, IJ05, IJ08, magnetic magnetic field in a soft consumptionfabrication IJ10, IJ12, IJ14, core electromagnetic magnetic core or yokeMany ink types Materials not IJ15, IJ17 fabricated from a can be usedusually present in a ferrous material such Fast operation CMOS fab suchas as electroplated iron High efficiency NiFe, CoNiFe, or alloys such asCoNiFe Easy extension CoFe are required [1], CoFe, or NiFe from singlenozzles High local alloys. Typically, the to pagewidth print currentsrequired soft magnetic material heads Copper is in two parts, whichmetalization should are normally held be used for long apart by aspring. electromigration When the solenoid is lifetime and low actuated,the two parts resistivity attract, displacing the Electroplating is ink.required High saturation flux density is required (2.0-2.1 T isachievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force actsas a IJ06, IJ11, IJ13, force acting on a current consumption twistingmotion IJ16 carrying wire in a Many ink types Typically, only a magneticfield is can be used quarter of the utilized. Fast operation solenoidlength This allows the High efficiency provides force in a magneticfield to be Easy extension useful direction supplied externally to fromsingle nozzles High local the print head, for to pagewidth printcurrents required example with rare heads Copper earth permanentmetalization should magnets. be used for long Only the currentelectromigration carrying wire need be lifetime and low fabricated onthe print- resistivity head, simplifying Pigmented inks materials areusually requirements. infeasible Magnetostriction The actuator uses theMany ink types Force acts as a Fischenbeck, giant magnetostrictive canbe used twisting motion U.S. Pat. No. 4,032,929 effect of materials Fastoperation Unusual IJ25 such as Terfenol-D (an Easy extension materialssuch as alloy of terbium, from single nozzles Terfenol-D are dysprosiumand iron to pagewidth print required developed at the Naval heads Highlocal Ordnance Laboratory, High force is currents required henceTer-Fe-NOL). available Copper For best efficiency, the metalizationshould actuator should be pre- be used for long stressed to approx. 8Mpa. electromigration lifetime and low resistivity Pre-stressing may berequired Surface Ink under positive Low power Requires Silverbrook, EPtension pressure is held in a consumption supplementary force 0771 658A2 and reduction nozzle by surface Simple to effect drop related patenttension. The surface construction separation applications tension of theink is No unusual Requires special reduced below the materials requiredin ink surfactants bubble threshold, fabrication Speed may be causingthe ink to High efficiency limited by surfactant egress from the Easyextension properties nozzle. from single nozzles to pagewidth printheads Viscosity The ink viscosity is Simple Requires Silverbrook, EPreduction locally reduced to construction supplementary force 0771 658A2 and select which drops are No unusual to effect drop related patentto be ejected. A materials required in separation applications viscosityreduction can fabrication Requires special be achieved Easy extensionink viscosity electrothermally with from single nozzles properties mostinks, but special to pagewidth print High speed is inks can beengineered heads difficult to achieve for a 100:1 viscosity Requiresreduction. oscillating ink pressure A high temperature difference(typically 80 degrees) is required Acoustic An acoustic wave is Canoperate Complex drive 1993 Hadimioglu generated and without a nozzlecircuitry et al, EUP 550,192 focussed upon the plate Complex 1993 Elrodet al, drop ejection region. fabrication EUP 572,220 Low efficiency Poorcontrol of drop position Poor control of drop volume Thermo- An actuatorwhich Low power Efficient aqueous IJ03, IJ09, IJ17, elastic bend reliesupon differential consumption operation requires a IJ18, IJ19, IJ20,actuator thermal expansion Many ink types thermal insulator on IJ21,IJ22, IJ23, upon Joule heating is can be used the hot side IJ24, IJ27,IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabricationprevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35,IJ36, IJ37, required for each Pigmented inks IJ38, IJ39, IJ40, actuatormay be infeasible, IJ41 Fast operation as pigment particles Highefficiency may jam the bend CMOS actuator compatible voltages andcurrents Standard MEMS processes can be used Easy extension from singlenozzles to pagewidth print heads High CTE A material with a very Highforce can Requires special IJ09, IJ17, IJ18, thermo- high coefficient ofbe generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermalexpansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator(CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30,polytetrafluoroethylene under development: which is not yet IJ31, IJ42,IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTEmaterials deposition (CVD), fabs are usually non- spin coating, and PTFEdeposition conductive, a heater evaporation cannot be followedfabricated from a PTFE is a with high conductive material is candidatefor low temperature (above incorporated. A 50 μm dielectric constant350° C.) processing long PTFE bend insulation in ULSI Pigmented inksactuator with Very low power may be infeasible, polysilicon heater andconsumption as pigment particles 15 mW power input Many ink types mayjam the bend can provide 180 μN can be used actuator force and 10 μmSimple planar deflection. Actuator fabrication motions include: Smallchip area Bend required for each Push actuator Buckle Fast operationRotate High efficiency CMOS compatible voltages and currents Easyextension from single nozzles to pagewidth print heads Conductive Apolymer with a high High force can Requires special IJ24 polymercoefficient of thermal be generated materials thermo- expansion (such asVery low power development (High elastic PTFE) is doped with consumptionCTE conductive actuator conducting substances Many ink types polymer) toincrease its can be used Requires a PTFE conductivity to about 3 Simpleplanar deposition process, orders of magnitude fabrication which is notyet below that of copper. Small chip area standard in ULSI Theconducting required for each fabs polymer expands actuator PTFEdeposition when resistively Fast operation cannot be followed heated.High efficiency with high Examples of CMOS temperature (above conductingdopants compatible voltages 350° C.) processing include: and currentsEvaporation and Carbon nanotubes Easy extension CVD deposition Metalfibers from single nozzles techniques cannot Conductive polymers topagewidth print be used such as doped heads Pigmented inks polythiophenemay be infeasible, Carbon granules as pigment particles may jam the bendactuator Shape A shape memory alloy High force is Fatigue limits IJ26memory such as TiNi (also available (stresses maximum number alloy knownas Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy Largestrain is Low strain (1%) developed at the Naval available (more than isrequired to extend Ordnance Laboratory) 3%) fatigue resistance isthermally switched High corrosion Cycle rate between its weak resistancelimited by heat martensitic state and Simple removal its high stiffnessconstruction Requires unusual austenic state. The Easy extensionmaterials (TiNi) shape of the actuator from single nozzles The latentheat of in its martensitic state to pagewidth print transformation mustis deformed relative to heads be provided the austenic shape. Lowvoltage High current The shape change operation operation causesejection of a Requires pre- drop. stressing to distort the martensiticstate Linear Linear magnetic Linear Magnetic Requires unusual IJ12Magnetic actuators include the actuators can be semiconductor ActuatorLinear Induction constructed with materials such as Actuator (LIA),Linear high thrust, long soft magnetic alloys Permanent Magnet travel,and high (e.g. CoNiFe) Synchronous Actuator efficiency using Somevarieties (LPMSA), Linear planar also require Reluctance semiconductorpermanent magnetic Synchronous Actuator fabrication materials such as(LRSA), Linear techniques Neodymium iron Switched Reluctance Longactuator boron (NdFeB) Actuator (LSRA), and travel is available Requiresthe Linear Stepper Medium force is complex multi- Actuator (LSA).available phase drive circuitry Low voltage High current operationoperation

BASIC OPERATION MODE Description Advantages Disadvantages ExamplesActuator This is the simplest Simple operation Drop repetition Thermalink jet directly mode of operation: the No external rate is usuallyPiezoelectric ink pushes ink actuator directly fields required limitedto around 10 kHz. jet supplies sufficient Satellite drops However, thisIJ01, IJ02, IJ03, kinetic energy to expel can be avoided if is notfundamental IJ04, IJ05, IJ06, the drop. The drop drop velocity is lessto the method, but is IJ07, IJ09, IJ11, must have a sufficient than 4m/s related to the refill IJ12, IJ14, IJ16, velocity to overcome Can beefficient, method normally IJ20, IJ22, IJ23, the surface tension.depending upon the used IJ24, IJ25, IJ26, actuator used All of the dropIJ27, IJ28, IJ29, kinetic energy must IJ30, IJ31, IJ32, be provided bythe IJ33, IJ34, IJ35, actuator IJ36, IJ37, IJ38, Satellite drops IJ39,IJ40, IJ41, usually form if drop IJ42, IJ43, IJ44 velocity is greaterthan 4.5 m/s Proximity The drops to be Very simple print Requires closeSilverbrook, EP printed are selected by head fabrication can proximitybetween 0771 658 A2 and some manner (e.g. be used the print head andrelated patent thermally induced The drop the print media orapplications surface tension selection means transfer roller reductionof does not need to May require two pressurized ink). provide the energyprint heads printing Selected drops are required to separate alternaterows of the separated from the ink the drop from the image in the nozzleby nozzle Monolithic color contact with the print print heads are mediumor a transfer difficult roller. Electrostatic The drops to be Verysimple print Requires very Silverbrook, EP pull printed are selected byhead fabrication can high electrostatic 0771 658 A2 and on ink somemanner (e.g. be used field related patent thermally induced The dropElectrostatic field applications surface tension selection means forsmall nozzle Tone-Jet reduction of does not need to sizes is above airpressurized ink). provide the energy breakdown Selected drops arerequired to separate Electrostatic field separated from the ink the dropfrom the may attract dust in the nozzle by a nozzle strong electricfield. Magnetic The drops to be Very simple print Requires Silverbrook,EP pull on ink printed are selected by head fabrication can magnetic ink0771 658 A2 and some manner (e.g. be used Ink colors other relatedpatent thermally induced The drop than black are applications surfacetension selection means difficult reduction of does not need to Requiresvery pressurized ink). provide the energy high magnetic fields Selecteddrops are required to separate separated from the ink the drop from thein the nozzle by a nozzle strong magnetic field acting on the magneticink. Shutter The actuator moves a High speed (>50 kHz) Moving parts areIJ13, IJ17, IJ21 shutter to block ink operation can required flow to thenozzle. The be achieved due to Requires ink ink pressure is pulsedreduced refill time pressure modulator at a multiple of the Drop timingcan Friction and wear drop ejection be very accurate must be consideredfrequency. The actuator Stiction is energy can be very possible lowShuttered The actuator moves a Actuators with Moving parts are IJ08,IJ15, IJ18, grill shutter to block ink small travel can be required IJ19flow through a grill to used Requires ink the nozzle. The shutterActuators with pressure modulator movement need only small force can beFriction and wear be equal to the width used must be considered of thegrill holes. High speed (>50 kHz) Stiction is operation can possible beachieved Pulsed A pulsed magnetic Extremely low Requires an IJ10magnetic field attracts an ‘ink energy operation is external pulsed pullon ink pusher’ at the drop possible magnetic field pusher ejectionfrequency. An No heat Requires special actuator controls a dissipationmaterials for both catch, which prevents problems the actuator and thethe ink pusher from ink pusher moving when a drop is Complex not to beejected. construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description AdvantagesDisadvantages Examples None The actuator directly Simplicity of Dropejection Most ink jets, fires the ink drop, and construction energy mustbe including there is no external Simplicity of supplied bypiezoelectric and field or other operation individual nozzle thermalbubble. mechanism required. Small physical actuator IJ01, IJ02, IJ03,size IJ04, IJ05, IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24,IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36,IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The inkpressure Oscillating ink Requires external Silverbrook, EP ink pressureoscillates, providing pressure can provide ink pressure 0771 658 A2 and(including much of the drop a refill pulse, oscillator related patentacoustic ejection energy. The allowing higher Ink pressure applicationsstimulation) actuator selects which operating speed phase and amplitudeIJ08, IJ13, IJ15, drops are to be fired The actuators must be carefullyIJ17, IJ18, IJ19, by selectively may operate with controlled IJ21blocking or enabling much lower energy Acoustic nozzles. The inkAcoustic lenses reflections in the ink pressure oscillation can be usedto focus chamber must be may be achieved by the sound on the designedfor vibrating the print nozzles head, or preferably by an actuator inthe ink supply. Media The print head is Low power Precision Silverbrook,EP proximity placed in close High accuracy assembly required 0771 658 A2and proximity to the print Simple print head Paper fibers may relatedpatent medium. Selected construction cause problems applications dropsprotrude from Cannot print on the print head further rough substratesthan unselected drops, and contact the print medium. The drop soaks intothe medium fast enough to cause drop separation. Transfer Drops areprinted to a High accuracy Bulky Silverbrook, EP roller transfer rollerinstead Wide range of Expensive 0771 658 A2 and of straight to the printprint substrates can Complex related patent medium. A transfer be usedconstruction applications roller can also be used Ink can be driedTektronix hot for proximity drop on the transfer roller meltpiezoelectric separation. ink jet Any of the IJ series Electrostatic Anelectric field is Low power Field strength Silverbrook, EP used toaccelerate Simple print head required for 0771 658 A2 and selected dropstowards construction separation of small related patent the printmedium. drops is near or applications above air Tone-Jet breakdownDirect A magnetic field is Low power Requires Silverbrook, EP magneticused to accelerate Simple print head magnetic ink 0771 658 A2 and fieldselected drops of construction Requires strong related patent magneticink towards magnetic field applications the print medium. Cross Theprint head is Does not require Requires external IJ06, IJ16 magneticplaced in a constant magnetic materials magnet field magnetic field. Theto be integrated in Current densities Lorenz force in a the print headmay be high, current carrying wire manufacturing resulting in is used tomove the process electromigration actuator. problems Pulsed A pulsedmagnetic Very low power Complex print IJ10 magnetic field is used tooperation is possible head construction field cyclically attract a Smallprint head Magnetic paddle, which pushes size materials required in onthe ink. A small print head actuator moves a catch, which selectivelyprevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description AdvantagesDisadvantages Examples None No actuator Operational Many actuatorThermal Bubble mechanical simplicity mechanisms have Ink jetamplification is used. insufficient travel, IJ01, IJ02, IJ06, Theactuator directly or insufficient force, IJ07, IJ16, IJ25, drives thedrop to efficiently drive IJ26 ejection process. the drop ejectionprocess Differential An actuator material Provides greater High stressesare Piezoelectric expansion expands more on one travel in a reducedinvolved IJ03, IJ09, IJ17, bend side than on the other. print head areaCare must be IJ18, IJ19, IJ20, actuator The expansion may be taken thatthe IJ21, IJ22, IJ23, thermal, piezoelectric, materials do not IJ24,IJ27, IJ29, magnetostrictive, or delaminate IJ30, IJ31, IJ32, othermechanism. The Residual bend IJ33, IJ34, IJ35, bend actuator convertsresulting from high IJ36, IJ37, IJ38, a high force low traveltemperature or high IJ39, IJ42, IJ43, actuator mechanism to stressduring IJ44 high travel, lower formation force mechanism. Transient Atrilayer bend Very good High stresses are IJ40, IJ41 bend actuator wherethe two temperature stability involved actuator outside layers are Highspeed, as a Care must be identical. This cancels new drop can be takenthat the bend due to ambient fired before heat materials do nottemperature and dissipates delaminate residual stress. The Cancelsresidual actuator only responds stress of formation to transient heatingof one side or the other. Reverse The actuator loads a Better couplingFabrication IJ05, IJ11 spring spring. When the to the ink complexityactuator is turned off, High stress in the the spring releases. springThis can reverse the force/distance curve of the actuator to make itcompatible with the force/time requirements of the drop ejection.Actuator A series of thin Increased travel Increased Some stackactuators are stacked. Reduced drive fabrication piezoelectric ink jetsThis can be voltage complexity IJ04 appropriate where Increasedactuators require high possibility of short electric field strength,circuits due to such as electrostatic pinholes and piezoelectricactuators. Multiple Multiple smaller Increases the Actuator forces IJ12,IJ13, IJ18, actuators actuators are used force available from may notadd IJ20, IJ22, IJ28, simultaneously to an actuator linearly, reducingIJ42, IJ43 move the ink. Each Multiple efficiency actuator need provideactuators can be only a portion of the positioned to control forcerequired. ink flow accurately Linear A linear spring is used Matches lowRequires print IJ15 Spring to transform a motion travel actuator withhead area for the with small travel and higher travel spring high forceinto a requirements longer travel, lower Non-contact force motion.method of motion transformation Coiled A bend actuator is Increasestravel Generally IJ17, IJ21, IJ34, actuator coiled to provide Reduceschip restricted to planar IJ35 greater travel in a area implementationsreduced chip area. Planar due to extreme implementations are fabricationdifficulty relatively easy to in other orientations. fabricate. FlexureA bend actuator has a Simple means of Care must be IJ10, IJ19, IJ33 bendsmall region near the increasing travel of taken not to exceed actuatorfixture point, which a bend actuator the elastic limit in flexes muchmore the flexure area readily than the Stress remainder of thedistribution is very actuator. The actuator uneven flexing iseffectively Difficult to converted from an accurately model even coilingto an with finite element angular bend, resulting analysis in greatertravel of the actuator tip. Catch The actuator controls a Very lowComplex IJ10 small catch. The catch actuator energy construction eitherenables or Very small Requires external disables movement of actuatorsize force an ink pusher that is Unsuitable for controlled in a bulkpigmented inks manner. Gears Gears can be used to Low force, low Movingparts are IJ13 increase travel at the travel actuators can requiredexpense of duration. be used Several actuator Circular gears, rack Canbe fabricated cycles are required and pinion, ratchets, using standardMore complex and other gearing surface MEMS drive electronics methodscan be used. processes Complex construction Friction, friction, and wearare possible Buckle plate A buckle plate can be Very fast Must staywithin S. Hirata et al, used to change a slow movement elastic limits ofthe “An Ink-jet Head actuator into a fast achievable materials for longUsing Diaphragm motion. It can also device life Microactuator”, converta high force, High stresses Proc. IEEE MEMS, low travel actuatorinvolved Feb. 1996, pp 418-423. into a high travel, Generally high IJ18,IJ27 medium force motion. power requirement Tapered A tapered magneticLinearizes the Complex IJ14 magnetic pole can increase magneticconstruction pole travel at the expense force/distance curve of force.Lever A lever and fulcrum is Matches low High stress IJ32, IJ36, IJ37used to transform a travel actuator with around the fulcrum motion withsmall higher travel travel and high force requirements into a motionwith Fulcrum area has longer travel and no linear movement, lower force.The lever and can be used for can also reverse the a fluid sealdirection of travel. Rotary The actuator is High mechanical Complex IJ28impeller connected to a rotary advantage construction impeller. A smallThe ratio of force Unsuitable for angular deflection of to travel of thepigmented inks the actuator results in actuator can be a rotation of thematched to the impeller vanes, which nozzle requirements push the inkagainst by varying the stationary vanes and number of impeller out ofthe nozzle. vanes Acoustic A refractive or No moving parts Large area1993 Hadimioglu lens diffractive (e.g. zone required et al, EUP 550,192plate) acoustic lens is Only relevant for 1993 Elrod et al, used toconcentrate acoustic ink jets EUP 572,220 sound waves. Sharp A sharppoint is used Simple Difficult to Tone-jet conductive to concentrate anconstruction fabricate using point electrostatic field. standard VLSIprocesses for a surface ejecting ink- jet Only relevant forelectrostatic ink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume Thevolume of the Simple High energy is Hewlett-Packard expansion actuatorchanges, construction in the typically required to Thermal Ink jetpushing the ink in all case of thermal ink achieve volume CanonBubblejet directions. jet expansion. This leads to thermal stress,cavitation, and kogation in thermal ink jet implementations Linear, Theactuator moves in Efficient High fabrication IJ01, IJ02, IJ04, normal toa direction normal to coupling to ink complexity may be IJ07, IJ11, IJ14chip surface the print head surface. drops ejected required to achieveThe nozzle is typically normal to the perpendicular in the line ofsurface motion movement. Parallel to The actuator moves Suitable forFabrication IJ12, IJ13, IJ15, chip surface parallel to the print planarfabrication complexity IJ33, IJ34, IJ35, head surface. Drop FrictionIJ36 ejection may still be Stiction normal to the surface. Membrane Anactuator with a The effective Fabrication 1982 Howkins push high forcebut small area of the actuator complexity U.S. Pat. No. 4,459,601 areais used to push a becomes the Actuator size stiff membrane that ismembrane area Difficulty of in contact with the ink. integration in aVLSI process Rotary The actuator causes Rotary levers Device IJ05, IJ08,IJ13, the rotation of some may be used to complexity IJ28 element, sucha grill or increase travel May have impeller Small chip area friction ata pivot requirements point Bend The actuator bends A very small Requiresthe 1970 Kyser et al when energized. This change in actuator to be madeU.S. Pat. No. 3,946,398 may be due to dimensions can be from at leasttwo 1973 Stemme differential thermal converted to a large distinctlayers, or to U.S. Pat. No. 3,747,120 expansion, motion. have a thermalIJ03, IJ09, IJ10, piezoelectric difference across the IJ19, IJ23, IJ24,expansion, actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33,IJ34, other form of relative IJ35 dimensional change. Swivel Theactuator swivels Allows operation Inefficient IJ06 around a centralpivot. where the net linear coupling to the ink This motion is suitableforce on the paddle motion where there are is zero opposite forces Smallchip area applied to opposite requirements sides of the paddle, e.g.Lorenz force. Straighten The actuator is Can be used with Requirescareful IJ26, IJ32 normally bent, and shape memory balance of stressesstraightens when alloys where the to ensure that the energized. austenicphase is quiescent bend is planar accurate Double The actuator bends inOne actuator can Difficult to make IJ36, IJ37, IJ38 bend one directionwhen be used to power the drops ejected by one element is two nozzles.both bend directions energized, and bends Reduced chip identical. theother way when size. A small another element is Not sensitive toefficiency loss energized. ambient temperature compared to equivalentsingle bend actuators. Shear Energizing the Can increase the Not readily1985 Fishbeck actuator causes a shear effective travel of applicable toother U.S. Pat. No. 4,584,590 motion in the actuator piezoelectricactuator material. actuators mechanisms Radial constriction The actuatorsqueezes Relatively easy High force 1970 Zoltan U.S. Pat. No. an inkreservoir, to fabricate single required 3,683,212 forcing ink from anozzles from glass Inefficient constricted nozzle. tubing as Difficultto macroscopic integrate with VLSI structures processes Coil/uncoil Acoiled actuator Easy to fabricate Difficult to IJ17, IJ21, IJ34, uncoilsor coils more as a planar VLSI fabricate for non- IJ35 tightly. Themotion of process planar devices the free end of the Small area Poorout-of-plane actuator ejects the ink. required, therefore stiffness lowcost Bow The actuator bows (or Can increase the Maximum travel IJ16,IJ18, IJ27 buckles) in the middle speed of travel is constrained whenenergized. Mechanically High force rigid required Push-Pull Twoactuators control The structure is Not readily IJ18 a shutter. Oneactuator pinned at both ends, suitable for ink jets pulls the shutter,and so has a high out-of- which directly push the other pushes it. planerigidity the ink Curl A set of actuators curl Good fluid flow DesignIJ20, IJ42 inwards inwards to reduce the to the region behind complexityvolume of ink that the actuator they enclose. increases efficiency CurlA set of actuators curl Relatively simple Relatively large IJ43 outwardsoutwards, pressurizing construction chip area ink in a chambersurrounding the actuators, and expelling ink from a nozzle in thechamber. Iris Multiple vanes enclose High efficiency High fabricationIJ22 a volume of ink. These Small chip area complexity simultaneouslyrotate, Not suitable for reducing the volume pigmented inks between thevanes. Acoustic The actuator vibrates The actuator can Large area 1993Hadimioglu vibration at a high frequency. be physically distant requiredfor et al, EUP 550,192 from the ink efficient operation 1993 Elrod etal, at useful frequencies EUP 572,220 Acoustic coupling and crosstalkComplex drive circuitry Poor control of drop volume and position None Invarious ink jet No moving parts Various other Silverbrook, EP designsthe actuator tradeoffs are 0771 658 A2 and does not move. required torelated patent eliminate moving applications parts Tone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages ExamplesSurface This is the normal way Fabrication Low speed Thermal ink jettension that ink jets are simplicity Surface tension Piezoelectric inkrefilled. After the Operational force relatively jet actuator isenergized, simplicity small compared to IJ01-IJ07, IJ10-IJ14, ittypically returns actuator force IJ16, IJ20, rapidly to its normal Longrefill time IJ22-IJ45 position. This rapid usually dominates returnsucks in air the total repetition through the nozzle rate opening. Theink surface tension at the nozzle then exerts a small force restoringthe meniscus to a minimum area. This force refills the nozzle. ShutteredInk to the nozzle High speed Requires IJ08, IJ13, IJ15, oscillatingchamber is provided at Low actuator common ink IJ17, IJ18, IJ19, inkpressure a pressure that energy, as the pressure oscillator IJ21oscillates at twice the actuator need only May not be drop ejection openor close the suitable for frequency. When a shutter, instead ofpigmented inks drop is to be ejected, ejecting the ink drop the shutteris opened for 3 half cycles: drop ejection, actuator return, and refill.The shutter is then closed to prevent the nozzle chamber emptying duringthe next negative pressure cycle. Refill After the main High speed, asRequires two IJ09 actuator actuator has ejected a the nozzle isindependent drop a second (refill) actively refilled actuators pernozzle actuator is energized. The refill actuator pushes ink into thenozzle chamber. The refill actuator returns slowly, to prevent itsreturn from emptying the chamber again. Positive ink The ink is held aslight High refill rate, Surface spill Silverbrook, EP pressure positivepressure. therefore a high must be prevented 0771 658 A2 and After theink drop is drop repetition rate Highly related patent ejected, thenozzle is possible hydrophobic print applications chamber fills quicklyhead surfaces are Alternative for:, as surface tension and requiredIJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20, IJ22-IJ45 operate torefill the nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description AdvantagesDisadvantages Examples Long inlet The ink inlet channel Designsimplicity Restricts refill Thermal ink jet channel to the nozzlechamber Operational rate Piezoelectric ink is made long and simplicityMay result in a jet relatively narrow, Reduces relatively large chipIJ42, IJ43 relying on viscous crosstalk area drag to reduce inlet Onlypartially back-flow. effective Positive ink The ink is under a Dropselection Requires a Silverbrook, EP pressure positive pressure, so andseparation method (such as a 0771 658 A2 and that in the quiescentforces can be nozzle rim or related patent state some of the ink reducedeffective applications drop already protrudes Fast refill timehydrophobizing, or Possible from the nozzle. both) to prevent operationof the This reduces the flooding of the following: IJ01-IJ07, pressurein the nozzle ejection surface of IJ09-IJ12, chamber which is the printhead. IJ14, IJ16, IJ20, required to eject a IJ22, , IJ23-IJ34, certainvolume of ink. IJ36-IJ41, IJ44 The reduction in chamber pressure resultsin a reduction in ink pushed out through the inlet. Baffle One or morebaffles The refill rate is Design HP Thermal Ink are placed in the inletnot as restricted as complexity Jet ink flow. When the the long inletMay increase Tektronix actuator is energized, method. fabricationpiezoelectric ink jet the rapid ink Reduces complexity (e.g. movementcreates crosstalk Tektronix hot melt eddies which restrict Piezoelectricprint the flow through the heads). inlet. The slower refill process isunrestricted, and does not result in eddies. Flexible flap In thismethod recently Significantly Not applicable to Canon restrictsdisclosed by Canon, reduces back-flow most ink jet inlet the expandingactuator for edge-shooter configurations (bubble) pushes on a thermalink jet Increased flexible flap that devices fabrication restricts theinlet. complexity Inelastic deformation of polymer flap results in creepover extended use Inlet filter A filter is located Additional Restrictsrefill IJ04, IJ12, IJ24, between the ink inlet advantage of ink rateIJ27, IJ29, IJ30 and the nozzle filtration May result in chamber. Thefilter Ink filter may be complex has a multitude of fabricated with noconstruction small holes or slots, additional process restricting inkflow. steps The filter also removes particles which may block thenozzle. Small inlet The ink inlet channel Design simplicity Restrictsrefill IJ02, IJ37, IJ44 compared to the nozzle chamber rate to nozzlehas a substantially May result in a smaller cross section relativelylarge chip than that of the nozzle, area resulting in easier ink Onlypartially egress out of the effective nozzle than out of the inlet.Inlet shutter A secondary actuator Increases speed Requires separateIJ09 controls the position of of the ink-jet print refill actuator and ashutter, closing off head operation drive circuit the ink inlet when themain actuator is energized. The inlet is The method avoids the Back-flowRequires careful IJ01, IJ03, IJ05, located problem of inlet back-problem is design to minimize IJ06, IJ07, IJ10, behind the flow byarranging the eliminated the negative IJ11, IJ14, IJ16, ink-pushingink-pushing surface of pressure behind the IJ22, IJ23, IJ25, surface theactuator between paddle IJ28, IJ31, IJ32, the inlet and the IJ33, IJ34,IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the The actuator and aSignificant Small increase in IJ07, IJ20, IJ26, actuator wall of the inkreductions in back- fabrication IJ38 moves to chamber are arranged flowcan be complexity shut off the so that the motion of achieved inlet theactuator closes off Compact designs the inlet. possible Nozzle In someconfigurations Ink back-flow None related to Silverbrook, EP actuator ofink jet, there is no problem is ink back-flow on 0771 658 A2 and doesnot expansion or eliminated actuation related patent result in inkmovement of an applications back-flow actuator which may Valve-jet causeink back-flow Tone-jet through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages ExamplesNormal All of the nozzles are No added May not be Most ink jet nozzlefiring fired periodically, complexity on the sufficient to systemsbefore the ink has a print head displace dried ink IJ01, IJ02, IJ03,chance to dry. When IJ04, IJ05, IJ06, not in use the nozzles IJ07, IJ09,IJ10, are sealed (capped) IJ11, IJ12, IJ14, against air. IJ16, IJ20,IJ22, The nozzle firing is IJ23, IJ24, IJ25, usually performed IJ26,IJ27, IJ28, during a special IJ29, IJ30, IJ31, clearing cycle, afterIJ32, IJ33, IJ34, first moving the print IJ36, IJ37, IJ38, head to acleaning IJ39, IJ40,, IJ41, station. IJ42, IJ43, IJ44,, IJ45 Extra Insystems which heat Can be highly Requires higher Silverbrook, EP powerto the ink, but do not boil effective if the drive voltage for 0771 658A2 and ink heater it under normal heater is adjacent to clearing relatedpatent situations, nozzle the nozzle May require applications clearingcan be larger drive achieved by over- transistors powering the heaterand boiling ink at the nozzle. Rapid The actuator is fired in Does notrequire Effectiveness May be used success-ion rapid succession. In extradrive circuits depends with: IJ01, IJ02, of actuator someconfigurations, on the print head substantially upon IJ03, IJ04, IJ05,pulses this may cause heat Can be readily the configuration of IJ06,IJ07, IJ09, build-up at the nozzle controlled and the ink jet nozzleIJ10, IJ11, IJ14, which boils the ink, initiated by digital IJ16, IJ20,IJ22, clearing the nozzle. In logic IJ23, IJ24, IJ25, other situations,it may IJ27, IJ28, IJ29, cause sufficient IJ30, IJ31, IJ32, vibrationsto dislodge IJ33, IJ34, IJ36, clogged nozzles. IJ37, IJ38, IJ39, IJ40,IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is A simple Notsuitable May be used power to not normally driven to solution wherewhere there is a with: IJ03, IJ09, ink pushing the limit of its motion,applicable hard limit to IJ16, IJ20, IJ23, actuator nozzle clearing maybe actuator movement IJ24, IJ25, IJ27, assisted by providing IJ29, IJ30,IJ31, an enhanced drive IJ32, IJ39, IJ40, signal to the actuator. IJ41,IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is A high nozzle HighIJ08, IJ13, IJ15, resonance applied to the ink clearing capabilityimplementation cost IJ17, IJ18, IJ19, chamber. This wave is can beachieved if system does not IJ21 of an appropriate May be alreadyinclude an amplitude and implemented at very acoustic actuator frequencyto cause low cost in systems sufficient force at the which alreadynozzle to clear include acoustic blockages. This is actuators easiest toachieve if the ultrasonic wave is at a resonant frequency of the inkcavity. Nozzle A microfabricated Can clear Accurate Silverbrook, EPclearing plate is pushed against severely clogged mechanical 0771 658 A2and plate the nozzles. The plate nozzles alignment is related patent hasa post for every required applications nozzle. A post moves Moving partsare through each nozzle, required displacing dried ink. There is risk ofdamage to the nozzles Accurate fabrication is required Ink The pressureof the ink May be effective Requires May be used pressure is temporarilywhere other pressure pump or with all IJ series ink pulse increased sothat ink methods cannot be other pressure jets streams from all of theused actuator nozzles. This may be Expensive used in conjunctionWasteful of ink with actuator energizing. Print head A flexible ‘blade’is Effective for Difficult to use if Many ink jet wiper wiped across theprint planar print head print head surface is systems head surface. Thesurfaces non-planar or very blade is usually Low cost fragile fabricatedfrom a Requires flexible polymer, e.g. mechanical parts rubber orsynthetic Blade can wear elastomer. out in high volume print systemsSeparate A separate heater is Can be effective Fabrication Can be usedwith ink boiling provided at the nozzle where other nozzle complexitymany IJ series ink heater although the normal clearing methods jets drope-ection cannot be used mechanism does not Can be require it. Theheaters implemented at no do not require additional cost in individualdrive some ink jet circuits, as many configurations nozzles can becleared simultaneously, and no imaging is required. NOZZLE PLATECONSTRUCTION Electro- A nozzle plate is Fabrication High Hewlett Packardformed separately fabricated simplicity temperatures and Thermal Ink jetnickel from electroformed pressures are nickel, and bonded to requiredto bond the print head chip. nozzle plate Minimum thickness constraintsDifferential thermal expansion Laser Individual nozzle No masks Eachhole must Canon Bubblejet ablated or holes are ablated by an required beindividually 1988 Sercel et drilled intense UV laser in a Can be quitefast formed al., SPIE, Vol. 998 polymer nozzle plate, which is Somecontrol Special Excimer Beam typically a polymer over nozzle profileequipment required Applications, pp. such as polyimide or is possibleSlow where there 76-83 polysulphone Equipment are many thousands 1993Watanabe required is relatively of nozzles per print et al., U.S. Pat.low cost head No. 5,208,604 May produce thin burrs at exit holes SiliconA separate nozzle High accuracy is Two part K. Bean, IEEE micro- plateis attainable construction Transactions on machined micromachined fromHigh cost Electron Devices, single crystal silicon, Requires Vol. ED-25,No. 10, and bonded to the precision alignment 1978, pp 1185-1195 printhead wafer. Nozzles may be Xerox 1990 clogged by adhesive Hawkins etal., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries No expensiveVery small 1970 Zoltan U.S. Pat. capillaries are drawn from glassequipment required nozzle sizes are No. 3,683,212 tubing. This methodSimple to make difficult to form has been used for single nozzles Notsuited for making individual mass production nozzles, but is difficultto use for bulk manufacturing of print heads with thousands of nozzles.Monolithic, The nozzle plate is High accuracy Requires Silverbrook, EPsurface deposited as a layer (<1 μm) sacrificial layer 0771 658 A2 andmicro- using standard VLSI Monolithic under the nozzle related patentmachined deposition techniques. Low cost plate to form the applicationsusing VLSI Nozzles are etched in Existing nozzle chamber IJ01, IJ02,IJ04, litho- the nozzle plate using processes can be Surface may beIJ11, IJ12, IJ17, graphic VLSI lithography and used fragile to the touchIJ18, IJ20, IJ22, processes etching. IJ24, IJ27, IJ28, IJ29, IJ30, IJ31,IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44Monolithic, The nozzle plate is a High accuracy Requires long IJ03,IJ05, IJ06, etched buried etch stop in the (<1 μm) etch times IJ07,IJ08, IJ09, through wafer. Nozzle Monolithic Requires a IJ10, IJ13,IJ14, substrate chambers are etched in Low cost support wafer IJ15,IJ16, IJ19, the front of the wafer, No differential IJ21, IJ23, IJ25,and the wafer is expansion IJ26 thinned from the back side. Nozzles arethen etched in the etch stop layer. No nozzle Various methods have Nonozzles to Difficult to Ricoh 1995 plate been tried to eliminate becomeclogged control drop Sekiya et al U.S. Pat. the nozzles entirely, toposition accurately No. 5,412,413 prevent nozzle Crosstalk 1993Hadimioglu clogging. These problems et al EUP 550,192 include thermalbubble 1993 Elrod et al mechanisms and EUP 572,220 acoustic lensmechanisms Trough Each drop ejector has Reduced Drop firing IJ35 atrough through manufacturing direction is sensitive which a paddlemoves. complexity to wicking. There is no nozzle Monolithic plate.Nozzle slit The elimination of No nozzles to Difficult to 1989 Saito etal instead of nozzle holes and become clogged control drop U.S. Pat. No.4,799,068 individual replacement by a slit position accurately nozzlesencompassing many Crosstalk actuator positions problems reduces nozzleclogging, but increases crosstalk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages ExamplesEdge Ink flow is along the Simple Nozzles limited Canon Bubblejet (‘edgesurface of the chip, construction to edge 1979 Endo et al GB shooter’)and ink drops are No silicon High resolution patent 2,007,162 ejectedfrom the chip etching required is difficult Xerox heater-in- edge. Goodheat Fast color pit 1990 Hawkins et sinking via substrate printingrequires al U.S. Pat. No. 4,899,181 Mechanically one print head perTone-jet strong color Ease of chip handing Surface Ink flow is along theNo bulk silicon Maximum ink Hewlett-Packard (‘roof surface of the chip,etching required flow is severely TIJ 1982 Vaught et shooter’) and inkdrops are Silicon can make restricted al U.S. Pat. No. 4,490,728 ejectedfrom the chip an effective heat IJ02, IJ11, IJ12, surface, normal to thesink IJ20, IJ22 plane of the chip. Mechanical strength Through Ink flowis through the High ink flow Requires bulk Silverbrook, EP chip, chip,and ink drops are Suitable for silicon etching 0771 658 A2 and forwardejected from the front pagewidth print related patent (‘up surface ofthe chip. heads applications shooter’) High nozzle IJ04, IJ17, IJ18,packing density IJ24, IJ27-IJ45 therefore low manufacturing cost ThroughInk flow is through the High ink flow Requires wafer IJ01, IJ03, IJ05,chip, chip, and ink drops are Suitable for thinning IJ06, IJ07, IJ08,reverse ejected from the rear pagewidth print Requires special IJ09,IJ10, IJ13, (‘down surface of the chip. heads handling during IJ14,IJ15, IJ16, shooter’) High nozzle manufacture IJ19, IJ21, IJ23, packingdensity IJ25, IJ26 therefore low manufacturing cost Through Ink flow isthrough the Suitable for Pagewidth print Epson Stylus actuator actuator,which is not piezoelectric print heads require Tektronix hot fabricatedas part of heads several thousand melt piezoelectric the same substrateas connections to drive ink jets the drive transistors. circuits Cannotbe manufactured in standard CMOS fabs Complex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, Waterbased ink which Environmentally Slow drying Most existing ink dyetypically contains: friendly Corrosive jets water, dye, surfactant, Noodor Bleeds on paper All IJ series ink humectant, and May jets biocide.strikethrough Silverbrook, EP Modern ink dyes have Cockles paper 0771658 A2 and high water-fastness, related patent light fastnessapplications Aqueous, Water based ink which Environmentally Slow dryingIJ02, IJ04, IJ21, pigment typically contains: friendly Corrosive IJ26,IJ27, IJ30 water, pigment, No odor Pigment may Silverbrook, EPsurfactant, humectant, Reduced bleed clog nozzles 0771 658 A2 and andbiocide. Reduced wicking Pigment may related patent Pigments have anReduced clog actuator applications advantage in reduced strikethroughmechanisms Piezoelectric ink- bleed, wicking and Cockles paper jetsstrikethrough. Thermal ink jets (with significant restrictions) MethylMEK is a highly Very fast drying Odorous All IJ series ink Ethylvolatile solvent used Prints on various Flammable jets Ketone forindustrial printing substrates such as (MEK) on difficult surfacesmetals and plastics such as aluminum cans. Alcohol Alcohol based inksFast drying Slight odor All IJ series ink (ethanol, 2- can be used wherethe Operates at sub- Flammable jets butanol, printer must operate atfreezing and others) temperatures below temperatures the freezing pointof Reduced paper water. An example of cockle this is in-camera Low costconsumer photographic printing. Phase The ink is solid at No dryingtime- High viscosity Tektronix hot change room temperature, and inkinstantly freezes Printed ink melt piezoelectric (hot melt) is melted inthe print on the print medium typically has a ink jets head beforejetting. Almost any print ‘waxy’ feel 1989 Nowak Hot melt inks aremedium can be used Printed pages U.S. Pat. No. 4,820,346 usually waxbased, No paper cockle may ‘block’ All IJ series ink with a meltingpoint occurs Ink temperature jets around 80° C. After No wicking may beabove the jetting the ink freezes occurs curie point of almost instantlyupon No bleed occurs permanent magnets contacting the print Nostrikethrough Ink heaters medium or a transfer occurs consume powerroller. Long warm-up time Oil Oil based inks are High solubility Highviscosity: All IJ series ink extensively used in medium for some this isa significant jets offset printing. They dyes limitation for use in haveadvantages in Does not cockle ink jets, which improved paper usuallyrequire a characteristics on Does not wick low viscosity. Some paper(especially no through paper short chain and wicking or cockle).multi-branched oils Oil soluble dies and have a sufficiently pigmentsare required. low viscosity. Slow drying Micro- A microemulsion is aStops ink bleed Viscosity higher All IJ series ink emulsion stable, selfforming High dye than water jets emulsion of oil, water, solubility Costis slightly and surfactant. The Water, oil, and higher than watercharacteristic drop size amphiphilic soluble based ink is less than 100nm, dies can be used High surfactant and is determined by Can stabilizeconcentration the preferred curvature pigment required (around of thesurfactant. suspensions 5%)

1. An inkjet printhead chip which comprises a wafer substrate; a drivecircuitry layer positioned on the wafer substrate; a plurality of nozzlechambers defined in the wafer substrate; a plurality of ink inletopenings defined in the wafer substrate, in fluid communication withrespective nozzle chambers; a plurality of nozzle chamber walls oppositerespective ink inlet openings and each defining an ink ejection port;and a plurality of ink ejection actuators connected to the drivecircuitry layer, at least one actuator being positioned in each wall andbeing displaceable into the respective nozzle chamber to reduce a volumeof the nozzle chamber and thus to eject ink from the nozzle chamber. 2.An inkjet printhead chip as claimed in claim 1, in which each nozzlechamber is the result of a crystallographic etch carried out on thewafer such that each nozzle chamber is frustoconical and tapers inwardlytowards the ink inlet opening.
 3. An inkjet printhead chip as claimed inclaim 2, which includes a number of ink ejection actuators positioned ineach wall, the wall including a nozzle rim that defines the ink ejectionport and the ink ejection actuators of each wall extending radiallytowards the nozzle rim.
 4. An inkjet printhead chip as claimed in claim3, in which each ink ejection actuator has an actuator arm of a materialthat has a coefficient of thermal expansion which is such that expansionof the actuator arm can be used to perform work and a heating circuitpositioned in the actuator arm such that, when the arm is heated, thearm experiences thermal differential expansion and is thus displacedinto the nozzle chamber.
 5. An inkjet printhead chip as claimed in claim4, in which an end of each actuator arm proximate the respective nozzlerim is displaceable into the nozzle chamber while an opposite end isfixed to the substrate.
 6. An inkjet printhead chip as claimed in claim4, in which each heater element is in the form of a serpentineelectrical heating element to facilitate substantially unhinderedexpansion of the actuator arm.
 7. An inkjet printhead as claimed inclaim 4, in which each heater element is of copper while each actuatorarm is of polytetrafluoroethylene.